Research Highlights

The concept of a black hole seems to be shrouded in mystery, perhaps partly because of the enigmatic name, but in reality it is a very simple one: a black hole is an object containing an enormous quantity of mass shrunk down to a tiny volume - so much so that the speed required to escape the pull of this compact object’s gravity would exceed even that of light.

One of the chief goals of current and planned astronomy surveys is to determine the nature of dark energy—the name given to the mysterious substance that appears to be making the expansion of the Universe proceed faster and faster over time in surprising opposition to the expectations of nearly all cosmologists only a couple of short decades ago. One technique to probe the nature of dark energy is to examine the distribution of matter in the Universe—essentially the universe’s clumpiness—and see how that distribution changes as we look farther and farther away from the Milky Way galaxy.

One of the more graphic terms in black hole physics is "spaghettification." It refers to the way that strongly varying gravitational forces can distort a round object into a shape most familiar from your dinner plate. This is a fate that can befall a star that has the misfortune to wander too close to a massive black hole. In this post, I want to tell you about some recent work I have done using computer simulations to explore how such stars get pulled and squashed as they fall into black holes. This work was done partly in order to understand whether we might soon be able to observe such events, in a nascent field of astronomy based on measuring gravitational waves.

In the hunt for dark matter, any information to help us narrow in on what to look for is key. Miguel Sánchez-Conde (KIPAC and Stockholm University) and Francisco Prada (IFT/UAM, Madrid) have just published a crucial clue, concerning the concentration of dark matter halos, which are self-gravitating accumulations of dark matter that host systems like galaxies and galaxy clusters. Their recent paper on “the flattening of the concentration-mass relation towards low halo masses and its implications for the annihilation signal boost” combines theoretical predictions with simulations to learn about Earth-mass to galaxy cluster-sized halos. “The point of the paper is to put together the theory and the [simulations],” says Sánchez-Conde.

Take a star that weighs about twice as much as our Sun, and compact it down to the size of a medium-sized city, to make a neutron star whose extreme mass warps the spacetime everywhere near it. Next, put a much smaller companion star in orbit around it at very close range, and let the system evolve: what happens now?

Astronomers strongly suspect that supermassive black holes play critical roles in the evolution of galaxies, but the details are not yet known. The masses of these monsters, when compared with the masses of their host galaxies, provide an important clue - but how do you weigh a black hole more than half way across the universe? KIPAC scientist Yashar Hezaveh has a great idea—and it involves using the most powerful radio telescope we have coupled to some new gravitational lenses.

I was searching for evidence of dark matter as my PhD thesis when I was a graduate student at The Ohio State University. While I was still developing my analysis, another team of researchers doing something similar thought there was a chance they had found this evidence of dark matter at the center of the Galaxy.

In order to properly design and construct LSST, and to effectively use its eventual data, scientists are devising sophisticated models to follow light through a complicated optical system that isn't yet built.

Example of ray bundle modeling for LSST: Image size (red) and measures of ellipticity (blue and purple) as a function of focal plane fine positioning relative to mirrors (z), for a simulated star image falling halfway to the outer edge of the focal plane

After a century of study, researchers still struggle to understand the origin of cosmic rays, particles with extreme energies that fill the Universe and bombard the Earth from all directions... On Tuesday at KIPAC@10, we asked: Where Did That Come From? and spent the morning talking about particle acceleration in the Universe. Afterwards, Luigi Tibaldo talked to Angela Olinto (KICP) and Neil Gehrels (NASA Goddard)

The Vela pulsar is in many ways the archetypal pulsar, one of nature's lighthouses where a rapidly spinning, highly magnetized neutron star sends out beams of particles and radiation sweeping through space like a beacon. Vela's proximity to Earth has allowed it to be studied in detail across the electromagnetic spectrum, including with radio waves, X-rays, and the highest energy "TeV" gamma rays. The latest contributions to our wealth of data on this phenomenon are the observations from the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope, the orbiting observatory in which KIPAC is the primary scientific institution. These observations have revealed an extended gamma-ray emitting structure surrounding the pulsar and coincident with a similarly extended area of radio emission, known as the "extended radio nebula," where electrons ejected from near the pulsar emit light through interactions with the ambient magnetic field.

Active galactic nuclei (AGN) are nature's extreme particle accelerators, where twin beams of high energy particles and radiation fly away from a supermassive black hole in the center of a distant galaxy. When one of the beams is pointed at us, we see the phenomenon of a blazar, which can be seen prominently in X-rays or gamma rays, the highest energy kinds of light. Observations with the Large Area Telescope of the Fermi Gamma-ray Space Telescope - which was built at SLAC and in which KIPAC is the main science institution - have revolutionized the study of blazars by cataloging their gamma-ray emission.